Intradermal injections are used for delivering a variety of diagnostic and treatment compositions into a patient. Substances may be injected intradermally for diagnostic testing, such as to determine a patient's immunity status against tuberculosis and the status of allergic diseases. Vaccines, drugs and other compounds may also be delivered intradermally. In many instances, intradermal delivery is preferred because it generally requires a smaller volume dose of the diagnostic or treatment compound than other delivery techniques. An intradermal injection is made by delivering the substance into the epidermis and upper layer of the dermis. There is considerable variation in the skin thickness, both between individuals and within the same individual at different sites of the body. Generally the outer skin layer, or the epidermis, has a thickness between 500-200 microns and the dermis, the inner and thicker layer of the skin, has a thickness between 1.5-3.5 mm.
Making intradermal injections is difficult and generally requires an experienced nurse or medical professional. Incorrect placement of the tip of the needle cannula leads to a failed injection. The placement of the needle tip deeper than about 3.0 mm has the potential of delivering the injection into the subcutaneous region, where the intradermal dosage may be insufficient. Incorrect placement of the needle cannula may also puncture the skin again after being inserted into dermis, with the delivered compound being lost on the surface of the skin. Injection is often followed by a jet effect, with the compound exiting the injection site through the needle puncture track. The jet effect is even more pronounced for injections through a needle placed perpendicular to the injection site and in particular for shallow delivery. The success of intradermal injections is often determined by the experience of the healthcare professional. The preferred intradermal injection technique (using a standard needle) requires the healthcare professional to stretch the skin, orient the needle bevel to face upward, and insert a short bevel needle cannula at an angle of around 10-15 degrees, assuring that 2 to 3 mm of the needle cannula are located in the skin. The needle tip ends up positioned in the dermis or close to epidermis boundary. The compound is slowly injected into the skin of the patient, forming a blister or wheal. The insertion of the needle at an incorrect angle and/or depth results in a failed intradermal injection. Intradermal (ID) injection has been considered for immunization in the past, but has generally been rejected in favor of more reliable intramuscular or subcutaneous routes of administration because of the difficulty in making a successful ID injection.
Administration into the region of the intradermal space has been routinely used in the Mantoux tuberculin test, in which a purified protein derivative is injected at a shallow angle to the skin surface using a 27 or 30 gauge needle and a standard syringe. The technique is known to be quite difficult to perform and requires specialized training A degree of imprecision in the placement of the injection results in a significant number of false negative test results. As a result, the Mantoux approach has not led to the use of intradermal injection for systemic administration of substances, despite the advantage of requiring smaller doses of substances.
There have been attempts to develop devices that would assure a precise needle penetration depth during ID injection which tends to vary due to tissue compliance, penetration angle, skill level and other factors. These are detailed in U.S. Pat. Nos. 4,393,870 20 and 6,200,291 and US Published Patent Applications no. 2003/0093032, 2004/0147901. These devices employ complex constructions that tension the skin by vacuum, expanding the mounting surface prior to the needle insertion.
Alchas et al. developed a unique intradermal needle assembly for the delivery of compounds into the intradermal space by penetrating the dermis perpendicularly to its surface. A limiter supporting the needle is placed on the skin, the needle inserted, and the compound delivered. The penetration depth is in the 0.5 to 3 mm range, with a device limiter setting the penetration depth. There is a broad range of patents, issued and pending, defining different features of the system. U.S. Pat. Nos. 6,494,865, 6,569,123, 6,689,118, 6,776,776 and others, and U.S. Patent Publication no. 2003/0199822 describe such systems. The main limitation of the systems developed by Alchas et al. is the broad range of deposit depth due to assembly tolerances, needle bevel and the variations in skin properties. Another concern is back flow through the needle channel from the deposit pool to the surface of the skin due to a short direct channel formed by the needle. The jet effect further limits the performance when a shallow delivery is attempted.
Shielding and disposal of the contaminated needle cannula is a primary concern upon completion of an injection. It is preferable to cover the contaminated needle as soon as the intradermal injection is completed. A number of different approaches to shielding the contaminated needle are discussed in U.S. Pat. Nos. 4,631,057, 4,747,837, 4,801,295, 4,998,920, 5,053,018, 5,496,288, 5,893,845 and others.
The lack of suitable devices to accomplish reproducible delivery to the epidermal and dermal skin layers has limited the widespread use of the ID delivery route. Using conventional devices, ID injection is difficult to perform, unreliable and painful to the subject. There is thus a need for devices and methods that will enable efficient, accurate and reproducible delivery of agents to the intradermal layer of skin.